In the batch production of ready-to-eat bran cereals wheat bran, flour, water, and other ingredients are mixed together with a flavor syrup, cooked, dumped onto a conveyor, processed by an extruder into strands, and then dried and toasted. The first step of this conventional process is the pressure cooking at about 260.degree. F. for one half hour of, for example, a 100 pound batch of wheat bran, 5 percent wheat flour, 7.5 pounds of an alternate flour and a flavoring material. The cooked mixture is extruded under low shear conditions into bran cereal nuggets or "buds" having a "fibrous" appearance. Products produced by this batch process generally stay crisp in milk for about 2-3 minutes. They then lose crispness and their integrity fairly rapidly, in milk or water. Rapid loss of integrity and crispness aids in use of the bran cereal for baking applications, such as in the production of bran cereal biscuits. However, it also may detract from the eating qualities or mouthfeel of the product when used as a breakfast cereal.
U.S. Pat. No. 4,500,558 to Fulger et al. relates to modification of bran by extrusion. In this patent, hereinafter referred to as the '558 patent, a bran and water feed having a bran to water ratio of from 5.5:1 to 10:1 is extruded in a counter-rotating twin-screw extruder under high temperature and high shear conditions. The modified bran according to this process is made more readily millable and, when milled, possesses a "mouthfeel" with an absence of grittiness and a greater "functionality" in a food product. The production of extruded nuggets is not taught.
U.S. Pat. No. 4,438,146, to Colby et al, relates to a method for preparing cooked wheat products. Here, an apparatus and method for cooking wheat products is shown wherein the products are cooked by extrusion through an extrusion die. The extruder is similar to a conventional twin screw extruding device, and the die plates, shown in FIGS. 2, 3, and 5, cause extrusion of the wheat product into strands.
Ground whole wheat is used and mixed with any desired dry ingredients. The cooked edible product is in expanded form. At column 3, lines 1-3, it is taught that an extrusion aid or lubricant may be added to the dough to modify the extrusion pressures. The preferred extrusion lubricant is an edible oil or fat, the extrusion itself providing the heat necessary for the expansion.
As seen in column 3 at lines 11-16, no external heat source is necessary, and because of steam vaporization upon extrusion, the die face itself is cooled so that the outer face of the die has a temperature in the range of 150.degree. F. to 180.degree. F.
Water and/or moisture containing product is added to the other ingredients in the cooker, the water being present in a range of 14 to 18 percent by weight. It is taught in the '146 patent that the level of moisture is important in relation to the development of heat in the die and to the achievement of the desired expansion. As taught at column 5, lines 39-43, the heating and cooking of the dough is primarily done in the die itself. This is also taught in column 5, lines 33-38, wherein it is stated that the heat generated during cooking in the die can require the temperature to be controlled such as with a water cooling jacket or the like around the body or barrel. Such cooling is to control the temperature range of dough entering the die to between ambient temperature (usually about 68.degree. F.-84.degree. F.) and about 180.degree. F. It is also stated in column 5, lines 27-29 that "cooking of the dough in the body or the barrel is not necessary and is to be minimized."
The dough, as taught in the '146 patent, in passing through the die generates heat sufficient to form steam and cook the dough enough to condition the gluten so that upon extrusion the dough expands in a desired form as determined by the die configuration. It is also taught that in the die itself the steam is superheated and reaches a temperature of about 250.degree. F. The fluid friction generates the heat.
U.S. Pat. No. 4,431,674 to Fulger et al relates to an all natural, ready-to-eat cereal derived from whole cereal grain. The process involves milling and separating the whole grain to produce several fractions, including a bran fraction, an endosperm fraction, and a germ fraction. The bran fraction and any bran material separated out from the ground germ is modified by high temperature, high pressure extrusion in a counter-rotating twin screw extruder.
In U.S. Pat. No. 3,682,652 to Corbin et al, a process for preparing a low calorie snack is taught. Here, corn or rice is mixed with water and then extruded under high pressure from the cooking section 13 to atmospheric pressure. Pressurized steam flashes off and inflates the starch mass to a matrix of tenderized dough which becomes firm with drying. Individual pieces are formed with a cut-off knife. The speed of the knives controls the length of the pieces.
In U.S. Pat. No. 2,120,138 to Mathews et al, a method for producing extruded food products is taught. This patent teaches that heat can be supplied in an extruder through the frictional resistance afforded during the grinding and extruding operations, and that in some instances this heat is sufficient for cooking. This patent also relates to an expanded edible product.
U S. Pat. No. 4,217,083 to Machuque discloses a twin-screw extruder for processing dough which includes a diffuser plate and a conical pressure equalization chamber between the tips of the extrusion screws and the nozzle assembly. These components are apparently included to equalize pressure over the nozzle apertures.
In U.S. Pat. No. 3,458,321, to Reinhart et al, a method for extrusion cooking of food products is taught. Here, a twin screw extruder is used. The extruder has a feed section, a cooking section, a devolatilizing section, water and heat are removed from the cooked material, the release of compressive force causing moisture to flash from the cooked material and thereby cool and partially dry the cooked material, which is then extruded. A cereal grain such as corn flour or the like is used, in combination with sugar and other ingredients. The dry ingredients are mixed together with a liquid within the twin screw cooking apparatus. Here, the mechanical forces of the twin screw extruder produce heat due to friction. The pressure applied to the food is taught as being over 1000 psi, and frequently several thousand psi. The food ingredient is gelatinized in the cooking section. Heat jackets are used around the casing 18. Cooling jackets can be used as well. The temperature range in the devolatization zone is approximately 200.degree. F. to about 325.degree. F. At the lower temperature, products are produced which are not puffed, while in the higher temperature range products are produced wherein some puffing has occurred. The temperature range in the metering zone F is between 105.degree. F. and 240.degree. F. The examples teach use of corn together with other ingredients including water. For example, in example I of the '321 patent, the water content raises the moisture to about 27 percent moisture by weight.
Canadian Patent No. 1,122,849 discloses a process for the processing of cereal mixtures comprising 40 to 90 percent bran and no more than 20 percent water, plus a binding agent (sugar, flour or starch) in a twin screw extruder to produce an extruded, expanded product.
U.S. Pat. No. 4,327,116 (Weith) discloses a bran bakery product made from dough composed of 100 parts by weight of bran, 200 to 300 parts by weight of water and 2.5 to 15 parts by weight of carob bean flour (or other vegetable thickening agent). Other conventional dough ingredients such as flavoring agents can be used. Weith specifically mentions wheat bran and rye bran.
U.S Pat. No. 4,350,714 (Duvall) teaches a corn bran, extrusion-cooked, expanded cereal which further contains corn flour, oat flour, ground limestone, [i.e., CaCO.sub.3 ], sugar, salt, soda, vitamin premix and colorant. Duvall states that wheat flour and rice flour can be present. Example 1 shows the use of 25 percent of corn bran flour, and the claims recite that sufficient ground corn bran is used to provide 3.5 to 10 weight percent of fiber. The extruded pieces are enrobed in a syrup which includes sugar, coconut oil and water.
British Patent No. 1,561,190 (Weetabix) discloses a food mixture containing bran and a binding agent (starchy material or gum) mixed with water. The mixture is extrusion cooked. The mixture (on a dry basis) contains 10 to 95 percent of bran. The mixture can also contain wheat and rice flours.
German O.S. No. 2,837,294 (Bories et al.) discloses an extrusion cooked foodstuff composed of bran, 20 to 80 percent; gluten, 5 to 20 percent, and the balance flour or starch, with the addition of 5 to 20 percent water after charging the mixture to an extruder.
According to Lineback et al., "Food Carbohydrates", (1982), page 296, there is not any completely satisfactory definition of the material which is generally referred to as fiber. The indigestible matter in animal feeds has always been designated as "crude fiber", and the term "dietary fiber" has been suggested for the plant cell wall constituents that are not digested by the secretions of the human digestive tract. The current definition of dietary fiber is not entirely satisfactory. There is a distinction between crude fiber and dietary fiber, since the former is a designation of a fraction determined analytically in a manner that gives an approximation of only cellulose and lignin and not of other cell-wall constituents not digested by man.
The substance that the lay public most readily equates with the term dietary fiber is wheat bran. Wheat bran is a heterogeneous substance which contains, in addition to fat and protein, at least 15 different minerals ranging from phosphorus and potassium at 1.04 and 1.38 percent, respectively, to iron (122 ppm), manganese (80 ppm), silicon (35 ppm) and selenium (0.1 ppm). Dietary fibers (or roughage) have been consumed for their laxative properties. The decreased intake of dietary fiber has been implicated as a factor in diseases such as cancer, diabetes and coronary disease.
The present invention provides a continuous process for the production of a high dietary fiber, ready-to-eat bran cereal in a cooker extruder. Upon exiting from the extruder die, the extrudate spontaneously breaks into spoon-sized strands, thereby eliminating the need for a cutting mechanism. The dried and toasted strands have uncut ends and an unplasticized, visibly roughened surface with visibly discrete bran particles. The cereal strands remain crisp in milk for at least 4 minutes. However, the strands lose their integrity in milk or water within less than about 15 minutes for use in baking.